A Comparison of Sub-Slab Soil Gas Measurements to Modeled Emissions from Subsurface Contamination

摘要

The vapor intrusion exposure pathway at a gasoline (benzene)-contaminated site in central Utah was evaluated using the U.S. EPA's November 2002 Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils. The vapor intrusion-to-indoor air pathway at this site was initially evaluated using the ASTM RBCA/Johnson & Ettinger modeling calculations. The modeling indicated that a potential unacceptable risk existed to occupants of a commercial building on the site. Subsequent sub-slab soil gas sampling conducted in accordance with the EPA's draft vapor intrusion guidance, however, indicated that the vapor intrusion pathway was not complete at this site. This paper will describe the site conditions, subsurface contamination, vapor intrusion modeling using the ASTM RBCA/Johnson & Ettinger Model and the VLEACH Model, and the sub-slab soil gas sampling results. The EPA's draft vapor intrusion guidance is not intended for use at leaking underground storage tank sites contaminated with petroleum hydrocarbons, however, the authors' felt that the approach made sense for this site. The EPA has formed a workgroup composed of EPA and State regulators to study the behavior of petroleum hydrocarbons in the subsurface and the vapor intrusion pathway.